Hi Gang,
Thank you so much for the advice!
I will definitely check out the paper soon (and yes, so each participant take one covariate value (e.g., RT)), and come back if I have further problems.
But essentially, I would set go for (1) 3-way interaction in the end (b/w-ss group x TENT x covariate) or go for (2) b/w-ss group x covariate interaction for each TENT basis? I presume to do the option (2), I would have to set the glf for each TENT..
Thank you again,
SJ